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    Combustion characteristics and performance of a Wankel engine for unmanned aerial vehicles at various altitudes
    (Elsevier Ltd, 2024) Kucuk, Merve; Sürmen, Ali; Şener, Ramazan
    This study investigates the effects of altitude on the combustion, emissions, and performance of a Wankel engine for unmanned aerial vehicles (UAVs). The main motivation behind the presented study is to contribute to the Wankel engine designs used as a power source in UAVs by revealing the operating conditions at various altitudes. For these purposes, a gasoline fueled Wankel engine was simulated at sea level conditions for different equivalence ratios and results were validated with their experimental counterparts. Then, CFD simulations were carried out at various altitudes (6000 ft, 10,000 ft, and 15,000 ft). The simulation results show that decreasing ambient air temperature, and pressure at higher altitudes reduces the fresh charge density, hence combustion efficiency and heat release rate (HRR). As a result, the performance characteristics such as the indicated mean effective pressure (IMEP), the indicated torque, and indicated power decrease and exhaust emissions increase. For 6000 rpm, IMEP decreases by 39.11%, 53.79%, and 69.22%, and the indicated power reduces by 35.51%, 52.47%, and 65.05% at the altitudes of 6000 ft, 10,000 ft, and 15,000 ft, respectively, compared to those obtained at the sea level conditions. As for exhaust emissions, CO and CO2 are lowest at sea level conditions and increase with altitude. © 2023 Elsevier Ltd
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    Effectiveness of hydrogen enrichment strategy for Wankel engines in unmanned aerial vehicle applications at various altitudes
    (Elsevier Ltd, 2024) Kucuk, Merve; Şener, Ramazan; Sürmen, Ali
    This study investigates the effectiveness of the hydrogen-enrichment strategy on a Wankel engine for unmanned aerial vehicles (UAVs). The primary motivation behind this study is to contribute to the Wankel-type rotary engine designs by revealing the influences of the hydrogen enrichment method on the Wankel engine performance at various altitudes. To achieve these objectives, CFD simulations were conducted by applying a hydrogen enrichment method to a neat gasoline Wankel engine model at sea level, 5000 ft and 15,000 ft altitudes. The hydrogen energy fraction at the intake was gradually increased from 0% to 10%. The decrease in ambient air temperature, pressure, density, and insufficient fresh charge with the increase in altitude leads to the reduced reference chamber temperature and pressure of the Wankel engine. Thus, the combustion worsens, the heat release rate (HRR) and performance decrease, also emissions deteriorate in these colder operating conditions. On the other hand, the unique physicochemical properties of hydrogen such as wide flammability limits, high homogeneity, relatively small quenching distance and high flame speed allow hydrogen-enriched mixture flames to propagate toward the narrower gaps in the combustion chamber and make up for some drawbacks of Wankel engines. As a result, flame propagation is accelerated and fuel burning rate, peak pressure and temperature values in the reference chamber are increased by hydrogen addition. For the cases at sea level with 5% and 10% hydrogen energy fraction, IMEP is increased by 6.59%, 8.50%, and the indicated power is increased by 35.51% and 52.47%. In the cases with the same energy fraction at 15,000 ft, IMEP is increased by 26.61% and 48.75%, and the indicated power is reduced by 26.61% and 48.75%, respectively. It has been proven that a small amount of hydrogen by energy fraction improves combustion efficiency and performance. The findings show that hydrogen has excellent compatibility with Wankel engines and hydrogen enrichment is a very practical concept for the improvement of the performance of these engines for UAVs. Thus, Wankel engines, which are already a very favorable power source for UAVs, become even more favorable by the hydrogen-blending strategy. © 2023 Hydrogen Energy Publications LLC